Device for optical monitoring of constituent in tissue or body fluid sample using wavelength modulation spectroscopy, such as for blood glucose levels

Abstract

A device for monitoring the concentration level of a constituent in tissue or a body fluid sample, such as glucose concentration in blood, has a laser light source which is modulated about a center emission frequency to probe the absorption spectrum of the constituent being monitored, a laser driver circuit for tuning and modulating the laser light, a photodetector for detecting light from the laser light source transmitted through the sample as the modulation frequency of the laser is tuned, and a demodulator for demodulating the transmitted light and detecting variations in magnitude at harmonics of the modulation frequency to assess the concentration level of that constituent. The device utilizes short-wavelength near-infrared laser light to monitor blood glucose levels, and could also be used for drug screening and diagnosis of other medical conditions as well. In one embodiment, the device is used to monitor blood glucose level externally from the body and non-invasively by trans-illumination through a thin layer of skin, without the need for physical penetration of the skin. In another embodiment, the device is used as an intravenous sensor deployed through a catheter, and its output can be used to control an insulin pump to stabilize the patient's blood glucose levels.

Description

[0001]This U.S. patent application claims the priority of U.S. Provisional Application No. 60 / 538,988 filed on Jan. 23, 2004, entitled “Non-Invasive Biomedical Sensor”, and U.S. Provisional Application No. 60 / 632,300, filed on Nov. 30, 2004, entitled “Continuous Intravenous Optical Glucose Monitor with Feedback Control for Insulin Pump”, of the same inventors.[0002]The subject matter herein was developed in part under a research grant provided by the U.S. Government, National Science Foundations, Grant / Project No. ECS01-34640, ORS No. R-2001906. The U.S. Government retains certain rights in the invention.TECHNICAL FIELD[0003]This invention generally relates to a device for optical monitoring of a constituent in tissue or body fluid sample, particularly for non-invasive or intravenous blood glucose monitoring.BACKGROUND OF INVENTION[0004]According to the American Diabetes Association, over 6% of the US population is affected by diabetes. Worldwide, the number of people with diabetes ...

AI Technical Summary

Benefits of technology

"The present invention is a device that can monitor a constituent in an aqueous sample by using wavelength-modulation absorption spectroscopy of a laser light probe and active signal processing to stabilize the laser probe, increase the signal-to-noise ratio, and decrease the calculations required. The device includes a laser light source, a laser driver circuit, a photodetector, and a demodulator. The device can be used for non-invasive monitoring of blood glucose levels, carbon dioxide levels, and other blood constituents. The device is portable, convenient, and can be used at home or at any location. The technical effects of the invention include improved accuracy and convenience of non-invasive blood glucose monitoring."

Problems solved by technology

Commercially available methods of monitoring glucose levels are invasive and prone to error.

The pain and risk of infection from invasive probes can often deter them from maintaining their prescribed monitoring schedule, escalating the risks of secondary aliments of diabetes mellitus.

However, such prior art devices have limitations that prevent their widespread use, e.g., lack of sensitivity and specificity, interference with other blood constituents and noise limitations.

Conventional noninvasive sensor systems for blood glucose monitoring still require frequent “finger-stick” blood glucose measurements for recalibration purposes, thus defeating its purpose to replace invasive methods.

However, this system is lacking in spectral referencing to completely eliminate spectral drifting of the optical system, and in the proper rationing of higher order derivative features to provide absolute glucose concentrations in varying portions of tissues.

One of the largest obstacles in non-invasive biomedical sensing is variability in the samples from person to person and from day to day.

Numerous variables must be analyzed simultaneously, requiring long and complex multivariate calculations to provide precise measurements of constituents.

The primary limitation of the multivariate analysis used in conventional measurement techniques is that if one of the components is estimated incorrectly, then the whole analysis can be skewed.

This inherent problem can be difficult to isolate and correct in real-time.

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